Stop syncing Modal system bars from Activity on Android

[zoontek]

Summary:

This PR removes updateSystemAppearance() and syncSystemBarsVisibility() along with their now-unused imports.

On Android, every time a <Modal> is shown, ReactModalHostView.updateSystemAppearance() reaches into the host activity's WindowInsetsController and copies its status bar / navigation bar style and visibility onto the dialog window. This was the only way to keep modal windows visually consistent with the activity, since native modules like StatusBarModule only operated on the activity window.

This is now obsolete:

• Add ExtraWindowEventListener interface #55721 added the ExtraWindowEventListener interface, letting native modules be notified when extra Windows (e.g. modal dialogs) are created and destroyed.
• Fix StatusBar modifications not applying to Modal windows on Android #56059 made StatusBarModule implement that interface, so status bar style and visibility now sync to modal windows directly from the module that owns them.

The navigation bar half of updateSystemAppearance() is owned by third-party libraries (expo-navigation-bar, @zoontek/react-native-navigation-bar). Their next releases will implement ExtraWindowEventListener the same way StatusBarModule does, syncing nav bar style and visibility to modal windows from the module that owns them.

At that point updateSystemAppearance() is fully redundant: every concern it covered is handled by the module responsible for that configuration.

Changelog:

[ANDROID] [REMOVED] - Remove manual system bar sync from ReactModalHostView; modal windows are now configured by modules implementing ExtraWindowEventListener (e.g. StatusBarModule).

Test Plan:

• Open a <Modal> on Android and confirm the status bar style matches the host activity (light / dark content), now driven by StatusBarModule's ExtraWindowEventListener.
• Change <StatusBar barStyle="light-content" /> / "dark-content" while a modal is open and confirm the change applies to the dialog window.
• Toggle <StatusBar hidden /> before and during a modal presentation and confirm the dialog stays in sync with the activity.

[meta-codesync]

@alanleedev has imported this pull request. If you are a Meta employee, you can view this in D106013785.